The present invention generally relates to an internal broaching machine. More specifically, the invention relates to an internal broaching machine which eliminates a gap between a broach and a pull head for gripping a front shank or pull end of the broach and a gap between the broach and a retrieving head for gripping a rear shank or follower end of the broach, thereby improving the accuracy of concentricity of the broach and the heads for a broaching operation.
When performing an inner surface broaching using a broach, a pull head has conventionally been used for holding a pull end of the broach, such as shown in JP-A-6-126526. FIG. 13 shows such a pull head. This pull head has a body 51 formed with an insertion hole 54 for a broach pull end 50 and four claw members 52 arranged radially around an axis of the body 51. The claw members 52 can be advanced into the insertion hole 54.
In operation, the broach pull end 50 is inserted into the insertion hole 54 of the pull head. Then, a sleeve 53 mounted on the pull head is slid toward the front end of the body 51, and an inward projecting portion 53a of the sleeve 53 pushes the claw members 52 into abutment against a reduced diameter portion 56 of the broach pull end 50. As a result, the broach pull end 50 is gripped by the claw members 52 in the insertion hole 54 and thus held in the body 51. Reference numeral 55 designates a spring that pushes back the sleeve 53.
In this conventional pull head, when the claw members 52 engage the reduced diameter portion 56 of the broach pull end 50, there is an axial play or gap between the reduced diameter portion 56 and the claw members 52. Further, when the broach is inserted, there is a radial play or gap between the reduced diameter portion 56, the claw members 52 and the inward projecting portion 53a of the sleeve 53. Thus, when the pull head clamps the broach, the broach is loosely movable.
The axial play between the reduced diameter portion 56 and the claw members 52 is removed when the broach pull end 50 is pulled down by the body 51. However, in the above process or during a broaching operation, the broach pull end 50 axially moves or vibrates relative to the body 51, adversely affecting machining accuracy and a life of the broach. With the conventional pull head, therefore, it is not possible to establish correct positioning between the broach and the pull head in the axial and radial directions.
Further, the conventional pull head does not hold the broach pull end 50 in a direction of its rotation.
A conventional method for restricting rotary movement of a broach shank involves, as shown in FIG. 14, forming a flat face 61 on a broach pull end 60 and a pin slot 64 in a body 62. After the broach pull end 60 is inserted, a pin 63 is inserted into the pin slot 64 in the body using an appropriate means to prevent rotation of the broach pull end 60. However, since a predetermined tolerance is requied in machining, a clearance 65 in the rotary direction is necessarily formed. As a result, when during a broaching operation the broach pull end 60 is pulled down by the body 62, the broach pull end 60 moves or vibrates in the rotary direction relative to the body 62.